1. Field of the Invention
The present invention relates to a communication system. More particularly, the present invention relates to an asynchronous transfer mode segmentation and reassembly interface ("ATM interface") which can be easily modified to accommodate different types of workstations and/or networks.
2. Description of the Prior Art
Over the last two decades, computer manufacturers generally are manufacturing resources compatible with decentralized, shared networks (e.g., local area networks). These decentralized networks allow information, typically restricted in form to one particular data type, to be shared between resources. With the emergence of multi-media communications, however, networks are now being required to support multiple data types. As a result, network manufacturers are tending to concentrate their efforts toward asynchronous transfer mode ("ATM") networking systems.
Referring to FIGS. 1 and 2, a conventional ATM networking systems 100 comprises a workstation 105 coupled to a network 110 (e.g., fiber optics, twisted pair or any other conventional medium) through a conventional ATM interface 115 and a physical device 120. The conventional ATM interface 115 and the physical device 120 are connected together through a plurality of unidirectional communication lines 125 configured in accordance with a well-known, standard ATM "Utopia" interface 130 (i.e. Universal Testing Operation Interface for ATM). This guarantees compatibility between the ATM interface 115 and the physical device 120.
One important function of the conventional ATM interface 115 and the physical device 120 is to accurately translate a "datagram" of information from a first data type supported by the workstation 105 into a standard format (e.g., an ATM cell) which can be transferred subsequently to other data types. Throughout the present application, a "datagram" is generally defined herein as a plurality of information bits in series.
Typically, as shown in FIG. 2, the workstation 105 internally processes data as a datagram having an arbitrary length, commonly referred to as a Service Data Unit ("SDU") 190. Thereafter, in order to transmit the SDU to a remotely located device coupled to the network 110, the workstation 105 performs operations on the SDU 190 to produce a protocol data unit ("PDU") 191 therefrom. The PDU 191 is a datagram having a variable bit length so as to include at least the SDU 190 and bytes of information such as padding 192 used for completely "filling" the PDU 191, control 193 and a Cyclic Redundancy Checkword 194 which is used to check that no errors occur in transmission, generally referred to as "PAD" information, "CNTL" information and "CRC", respectively.
The conventional ATM interface 115 converts the PDU 191 into at least one ATM cell 195 depending on the size of the PDU 191. If the PDU 191 has a maximum of forty (40) bytes of data, the conventional ATM interface 115 produces one ATM cell. Otherwise, the conventional ATM interface 115 produces a sequence of ATM cells wherein only the last of the sequence of ATM cells include the CNTL information 193 and CRC 194 and at most the last two ATM cells may include PAD information 192.
Still referring to FIG. 2, each ATM cell 195 includes a four (4) byte header 196 for indicating a designated "target" location of its corresponding ATM cell 195 and a one (1) error byte 197 which is used to monitor for errors in transmitting the header. The error byte 197 is provided by a physical layer of the physical device 120 (discussed below). Moreover, each of the ATM cells 195 includes a forty-eight (48) byte "payload" 198 which solely includes data of the PDU 191 until the last few ATM cells as discussed above.
Referring back to FIG. 1, the physical device 120 consists of a physical layer 135 and a physical media dependency ("PMD") 140, collectively operating as both a transmitter and a receiver, to propagate information between the network 110 and the workstation 105. With respect to the transmitting operations, the conventional ATM interface 115 serially transmits the ATM cells to the physical layer 135. The physical layer 135 converts these ATM cells into a bit stream which is input into the PMD 140. The PMD 140 formats the bit stream according a particular data type used by the network 110. The physical device 120 operates in an opposite manner for the receiving operation.
More specifically, the conventional ATM interface 115 provides a reception signal path 146 and a transmission signal path 147, both of which including in series a pair of state machines working in combination with a storage queue (e.g., a First-In, First-Out "FIFO" queue). For the reception signal path 146, a receiver ("RX") state machine 150 receives an ATM cell from the physical layer 135. Then, the RX state machine 150 (i) removes the header portion of the ATM cell, (ii) performs CRC calculations on the payload of the ATM cell and if no transmission errors, (iii) transfers the payload into a first storage queue (e.g., a First-In, First-Out queue) 155 for temporary storage. Upon receipt of appropriate control signals, the first storage queue 155 transfers the payload through a system bus interface 170 and onto a system bus 165 for appropriate storage in the memory element 145. This transfer is controlled by a first interface state machine 160.
Additionally, for the transmission signal path 147, the memory element 145 places information onto the system bus 165 addressed to be transferred through the system bus interface 170 and into a second storage queue 180. Under control of the second interface state machine 175, the second storage queue 180 outputs the information into a transmitter ("TX") state machine 185 for transmission through the Utopia interface 130 and into the physical device 120.
This implementation for the ATM interface has a number of disadvantages. One disadvantage is that the conventional ATM interface is not easily modifiable (i.e., scalable) to accommodate for different capabilities of the workstation and/or the selected network. For example, if the operational speed of the network is increased from 616 mega-bits-per-second ("Mbps") to 1.2 giga-bits-per-second("Gbps"), the entire architecture of the conventional ATM interface would likely be required to be completely re-designed to allow for the increased throughput.
Another reason is that the conventional ATM interface is not "reusable" i.e., the architecture does not support a wide variety of workstation and network configurations.
Yet another disadvantage is that the conventional ATM interface arbitrates for ownership of the system bus of the workstation rather than using scheduling techniques. This may lead possible arbitration problems between transmission and reception elements. Thus, it would be desirous to provide an ATM interface that overcomes the above-identified advantages.